Metal cans, such as those used to package soft drinks and beer, have at least one end that is separately manufactured and attached to the remainder of the can body. In a two-piece can, the body of the can is drawn and ironed so as to integrally form sidewalls and a bottom. A separate can end is manufactured by forming a side wall, referred to as the "chuck wall," and a curled seaming panel into a metal blank. The seaming panel is then attached to the can body sidewall by a seaming operation. Because of the internal pressure within the can, the can end must have a high degree of stiffness in order to avoid undergoing excessive deformation. However, in order to achieve economical production, it is important that the metal be as thin as possible. Consequently, can makers strive to reduce the thickness of the can end without sacrificing strength.
In the past, it was found that the stiffness of the can end could be increased by "re-forming" the metal blank so as to include an annular countersink or anti-peaking bead. The bead is formed by inner and outer conical walls connected by a circular arcuate section. Initially, such annular beads were formed by placing the metal blank between upper and lower dies and essentially coining or stamping the bead into the metal. Such a method is disclosed, for example, in U.S. Pat. No. 3,537,291 (Hawkins), assigned to Reynolds Metals Company, U.S. Pat. No. 3,957,005 (Heffner), assigned to Aluminum Company of America, U.S. Pat. No. 4,217,843 (Kraska), assigned to National Can Corporation, and U.S. Pat. Nos. 4,865,506 (Kaminski) and 5,149,238 (McEldowney), assigned to Stolle Corporation, the disclosures of each of which is hereby incorporated by reference in its entirety. However, unless the radius of curvature of the arcuate section was fairly large, forcing the metal into a precisely pre-determined shape, as occurs in such stamping or coining methods, leads to cracking of the metal.
Various approaches have been tried in an effort to overcome the drawbacks of the stamping/coining method. In one approach, an annular bead is formed by drawing the metal around a tool having a radiused support surface, such as an annular nose formed in the periphery of a punch. This approach is disclosed in U.S. Pat. No. 4,574,608 (Bulso), assigned to Redicon Corporation, and U.S. Pat. No. 4,735,863 (Bachmann), assigned to Dayton Reliable Tool Corporation, the disclosure of each of which is hereby incorporated by reference in its entirety. However, particularly when the radius of curvature of the arcuate section is small, this method results in excessive thinning of the metal in the arcuate section--that is, at the crown of the bead. Another approach involved initially drawing a can end blank and then reversing the direction of travel of the tooling so as to essentially fold a portion of the chuck wall back on itself, thereby forming an annular bead. This approach is disclosed in U.S. Pat. No. 4,109,599 (Schultz), assigned to Aluminum Company of America, U.S. Pat. No. 4,722,215 (Taube), assigned to Metal Box, plc, U.S. Pat. No. 4,808,052 (Bulso), assigned to Redicon Corporation, and U.S. Pat. No. 4,934,168 (Osmanski), assigned to Continental Can Company, the disclosure of each of which is hereby incorporated by reference in its entirety. However, the narrowness of the bead and the tightness of the radius of curvature of the arcuate section that could be obtained using this method was limited.
More recently, efforts have been made to improve the bead by initially fully forming a bead in a first operation and then reworking the bead in a second operation to reduce its the width and radius of curvature. Once such approach reworks the bead by stamping it between a punch and a die, such as disclosed in U.S. Pat. No. 4,031,837 (Jordan), assigned to Aluminum Company of America, and U.S. Pat. No. 5,685,189 (Nguyen), assigned to Ball Corporation. However, forcing the metal into a predetermined shape in this manner often results in cracking, as previously discussed. In another approached, the bead is reworked by drawing metal around a tool having a small radiused support surface. This approach is disclosed in U.S. Pat. No. 4,559,801 (Smith), assigned to Ball Corporation, and U.S. Pat. No. 5,356,256 (Turner). However, drawing the metal tightly around a tool can result in excessive thinning, which weakens the bead and defeats the purpose of the reworking operation. Still another approach, disclosed in U.S. Pat. No. 4,991,735 (Biondich), assigned to Aluminum Company of America, involves buckling the bead. However, such buckling is inherently unpredictable and, therefore, difficult to control.
Moreover, in many proposed methods for reworking the bead, such as that disclosed in U.S. Pat. No. 4,031,837 (Jordan), discussed above, neither the chuck wall nor seaming panel is constrained during the reworking. This results in loss of dimensional control over the precise location of the bead. Also, although it has been proposed to reduce the width of the bead in the same station in which the bead is initially formed--see, for example, U.S. Pat. No. 4,715,208 (Bulso), assigned to Redicon Corporation, and U.S. Pat. No. 5,046,637 (Kysh), assigned to CMB Foodcan, plc--such an approach imposes limitations on the tooling that may be used to effect the reworking and requires complex tooling design with respect to the number of moving parts.
Consequently, it would be desirable to provide a method and apparatus for reducing the width and/or radius of curvature of an annular bead in a can end that did not result in cracking or excessive thinning of the metal and that was able to maintain close control of the location of the bead.